Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
  Case Tag  
Price  
Sales  
Tax %  
Raw Total  
Incl. Sales Tax  
Rounded  
to Penny  
Rounded  
to Nickel  
Rounded  
to Dime  
  Purchase #1 $236.27   12.174%   $265.0335   $265.03   $265.05   $265.00  
  Purchase #2 $184.82   3.463%   $191.2203   $191.22   $191.20   $191.20  
  Purchase #3 $136.55   6.143%   $144.9383   $144.94   $144.95   $144.90  
  Purchase #4 $41.86   9.320%   $45.7614   $45.76   $45.75   $45.80  
  Purchase #5 $117.79   11.371%   $131.1839   $131.18   $131.20   $131.20  
  Purchase #6 $24.69   8.471%   $26.7815   $26.78   $26.80   $26.80  
  Purchase #7 $231.61   11.484%   $258.2081   $258.21   $258.20   $258.20  
  7 purchase totals = $973.59       $1,063.1270   $1,063.12   $1,063.15   $1,063.10